Seems like the Model 66 is a favorite of many, me included. I also have one, a M66-1. Bought it new in the box at a gun show, it's from 1981. I liked it well enough to make it my EDC, put a set of Altamont stock on it so I could keep the factory ones in nice shape.
My real favorites, though, are my pair of .41 Magnums. A Model 57, "S" prefix, from 1968, and a Model 58 "S" prefix, from 1967. The M58 is another ANIB purchase, spent its whole life in two different safes until I picked it up from the 2nd owner.
My most favorite of all. The S&W 686 that rode with me many miles on duty for 8 years. A glass smooth trigger from years of monthly range sessions and is very accurate. Purchased for $150 when the department changed over to Glocks. I still have a 686-2 that I purchased at the same time that had never been issued for $150 also. It’s still in original box unfired.
But this one is an old friend! It even has a few patrol unit seat belt buckle scratches on the right side plate.